Use of fuzzy probability theory to assess spalling occurrence in underground openings

Spalling is an unstable phenomenon of rock surrounding underground openings that are subject to high in situ stress, along with the development of fractures. Up until now, spalling criteria have been developed based on experience in the field; however, the range of values in all spalling criteria is in either case or site dependent such that fuzziness or vagueness cannot be avoided. In this study, a new fuzzy probability model to assess systematically the probability of spalling in early design stage is proposed. Twenty underground opening projects across the world were evaluated using the proposed method. Results expressed in terms of spalling probability agreed well with field observations. In particular, the new fuzzy probability model, which considers all three spalling criteria by adopting weighting factors, was able to resolve the problem of erroneous assessment of spalling when only one spalling criterion is chosen.